Audiences for content blocks, such as broadcast media or online streamed media, including commercial advertising, are typically measured via single-source data panels consisting of individuals or households recording content exposure over time. In one typical system, panel members carry a portable pager-sized device with a microphone that listens for embedded subaudible codes or watermarks in audio of media programs. The device records the codes it hears, indicating that the panel member was present while the program was being shown or played. The device periodically transmits its logs to a measurement server, which aggregates logs from a plurality of the devices to determine a total viewership for the program.
As the codes or watermarks used by these devices must be inaudible or psychoacoustically concealed within the program, error rates are high and bitrates of data are very low. The device must listen to the audio signal for a substantial duration to be able to collect a complete code, reducing its effectiveness for short programs. Additionally, because codes must be embedded into the audio signal by the broadcaster, each broadcast station or cable provider must have an encoder in the signal chain, increasing cost and providing a potential source of failure.